An LED (light emitting diode) generally includes a diode mounted onto a die or chip. The diode is then surrounded by an encapsulant. The die receives electrical power from a power source and supplies power to the diode. The die can be mounted in a die support. To produce a brighter LED, generally, more power is delivered to the LED.
Many LED lighting systems dissipate heat through a different heat transfer path than ordinary filament bulb systems. More specifically, high power LED lighting systems dissipate a substantial amount of heat via a cathode (negative terminal) leg or through the die attached in a direct die mount device. The conventional heat dissipation systems (i.e. radiating a large percentage of heat to a front lens of a lamp) do not adequately reduce heat in higher power LED systems. Consequently, high power LED systems tend to run at high operating temperatures.
High operating temperatures degrade the performance of the LED lighting systems. Empirical data has shown that LED lighting systems may have lifetimes approaching 50,000 hours while at room temperature; however, operation at close to 90° C. may reduce an LED life to less than 7,000 hours.
To use high brightness LEDs in small lighting footprints, some degree of active cooling can facilitate reducing the temperature of the LED and thus the overall light fixture size since a large heat sink is not necessary. Spot cooling using a fan is known. A known fan includes a flexible diaphragm mounted around its entire periphery to a rigid housing defining an internal chamber. The diaphragm includes an orifice. The diaphragm moves in and out of the internal chamber as it is being actuated by a piezoelectric actuator.
As the diaphragm moves into the chamber, decreasing the chamber volume, fluid is ejected from the chamber through the orifice. As the fluid passes through the orifice, the flow separates at the sharp edges of the orifice and creates vortex sheets which roll up into vortices. These vortices move away from the edges of the orifice under their own self-induced velocity.
As the diaphragm moves out of the chamber, increasing the chamber volume, ambient fluid is drawn into the orifice, and thus into the chamber. Since the vortices are already removed from the edges of the orifice, they are not affected by the ambient fluid being entrained into the chamber. As the vortices travel away from the orifice, they synthesize a jet of fluid, a “synthetic jet,” through entrainment of the ambient fluid. It is these fans or synthetic jet generators that have been found useful in cooling electronic packages.
Known piezoelectric fans and synthetic jet actuators have relatively limited capacity, in that they use only a single moving element or a moving element of limited deflection. It would be desirable to increase the performance of an LED assembly by providing an active cooling system that overcomes the above mentioned shortcomings.